For the second year in a row, Massachusetts lawmakers June 14 endorsed a proposal to extract an estimated $2 billion from the state's roughly 20,000 highest earners, setting up a 2018 ballot question campaign, a legal dispute in the state's highest court, or both.

Rep. Jay Kaufman, a Lexington Democrat and House chairman of the Revenue Committee, said establishing a 4 percent surtax on incomes over $1 million would give Massachusetts a fairer system of government funding and inject money into public education and transportation.

The state's constitution requires income taxes be levied uniformly, so activists have backed the tax measure as a constitutional amendment. The vote of 134-55 means that voters will have the ultimate say on the proposed tax unless the Supreme Judicial Court determines the question is unconstitutional.

If it reaches the ballot and is approved, the proposal would facilitate a major tax increase without lawmakers having to vote directly on the proposal, or having to deal with possible objections from Republican Gov. Charlie Baker.

The top senators of both parties agreed that the amendment is likely to be taken up by the Supreme Judicial Court, but they are of different minds about how the court would likely decide the matter.

The proposed amendment (S 10) specifies that the revenues collected could "only" be spent to provide "quality public education and affordable public colleges and universities, and for the repair and maintenance of roads, bridges and public transportation."

Senate Minority Leader Bruce Tarr, a Gloucester Republican, suggested the question would run afoul of the constitutional prohibition against initiative petitions making a "specific appropriation of money."

"I'm fairly confident that there will be a case about its constitutionality," Tarr said. He said his analysis is that the question is "not properly before us" but that it would be "for the court to decide."

"The opponents have a right to challenge it, and I am expecting that they will," Senate President Stan Rosenberg, an Amherst Democrat, said after the vote. He said, "The proponents worked closely with constitutional experts and they believe this will stand up to constitutional muster."

The state Department of Revenue (DOR) released a report in September 2016 with the number of residents, by municipality, who have filed income taxes with an adjusted gross income of more than $1 million. The DOR statistics reflected 2014 incomes. Click on each city or town to learn more about how many million dollar earners live in the community.

According to information from the state Department of Revenue, 66 Bedford residents, less than 1 percent of the town's population, reported yearly income over $1 million. Rep. Ken Gordon, D-Bedford, supported the amendment, citing the improvements it could make in needed areas.

"The transportation area is something that we could really use the money for, in my communities of Bedford, Burlington and Wilmington, transportation is a big concern. If you were to ask residents what their biggest concern is in the community, the most popular answer would be the amount of traffic," Gordon said. "People are looking to get to work and if we get more money for publicly funded transportation, that will help improve the situation."

The measure passed the constitutional convention June 14 by a slightly higher margin than last year, when it passed 135-57.

Gordon doesn't believe imposing the tax would discourage high-earning residents from moving to Massachusetts, arguing the improvements to education and transportation would make the state a more attractive location for companies and residents.

"Big companies want to be where the education system is strong, that is why you see businesses headquartered in Cambridge, or in Silicon Valley because that is where the education is," Gordon said. "Improvements to both our education and transportation systems will attract more companies, which will attract new residents as well because the reason people really move is because of work."

House Minority Leader Brad Jones hearkened to 2013 when the Legislature passed a bill applying the sales tax to certain computer services before repealing the law a few months later. The North Reading Republican wondered aloud what lawmakers would do if they determined the income surtax was ill-conceived.

"What do you do to fix it? My understanding is it's a four-year process to fix that mistake," said Jones, who called the proposal a "poll-tested, focus-group-approved public policy."

"We can't go back and three months later turn the dial back, because it will be in our constitution, enshrined, and that is something we can't change," said Plymouth Republican Sen. Vinny deMacdeo.

The tax proposal is a citizen petition backed by Raise Up Massachusetts, a progressive group that has scored wins at the ballot and in the Legislature on raising the minimum wage and guaranteeing workers earned sick time.

Saying lawmakers "owe a debt of gratitude" to Raise Up, Kaufman told his colleagues that people on the lower rungs of the income scale expend 10 percent of their earnings in state and local taxes, while the wealthiest Bay Staters pay less than 5 percent of their income in state and local taxes.

"That is the classic definition of a regressive tax system," said Kaufman.

Kaufman said 99.5 percent of state residents would be unaffected by the new tax, except for what he said would be an enhancement in state services. He said for incomes over $1 million, the tax would cost $40,000, which he said would be about $30,000 after a federal offset.

Republicans countered that the income tax is the least regressive of the state's taxes, and that relying on such a small number of the highest earners to fund transportation and educational needs would put state finances in a precarious position. Speaking over the din of the crowded chamber, Republicans also accused their colleagues of abdicating their responsibility to decide questions of taxation.

Brockton Democrat Sen. Michael Brady, the Senate chair of the Revenue Committee, said lawmakers' role is to give voters a chance to vote on the plan. While lawmakers are actively working to raise marijuana taxes and impose taxes on short-term rentals, he said there are "no other realistic revenue sources."

Tax revenues counted on to support the state's roughly $40 billion fiscal 2017 budget have fallen short by almost $500 million.

"With the Fair Share Amendment on the ballot, we now have a once-in-a-generation chance to make critical investments in transportation and public education that increase economic opportunity for the people of Massachusetts," Lew Finfer, co-chair of Raise Up Massachusetts, stated.

Rep. Paul Frost, an Auburn Republican, highlighted a GOP-backed amendment to the question that was shot down last session and would have specified that any funds raised through the surtax would be allocated on top of -- not in place of -- existing spending. He said he expects that any money generated will be diverted to other purposes.

"We have seen in the past when times get tough that trust funds and dedicated revenues for certain programs get raided to be put elsewhere in the budget," he said.

"The proposed historic tax increase represents an unprecedented move to shelter elected politicians from accountability for taxation and spending policies," Massachusetts High Technology Council President Chris Anderson stated. "But before the special-interest-backed measure, which would prove disastrous to our goals of economic growth and job creation, heads to the ballot -- it must first pass constitutional muster. We believe it will fail that test."

Tarr said he believes the High Tech Council has a "consortium of folks that are contemplating who is the best plaintiff group and how to move forward" with a legal challenge to the proposal.

Katie Lannan contributed reporting. Caitlyn Kelleher and Jesse Collings of Wicked Local also contributed to this report.